1. Field of the Invention
This invention lies in the field of combustion of high sulphur containing fuels, with combustion gases containing substantial amounts of sulphur trioxide.
Still further, this invention involves means for the elimination of plumes of smoke from stacks, where the smoke plume has coloration other than the shades of black and grey, which are typical of the burning of combustible gases. Such plumes result from combustion of fuels which contain too-great quantities of sulphur. Cause of the plume is well known and is due to the presence of sulphur trioxide in the combustion gases as they are finally vented to the atmosphere.
2. Description of the Problem
When there is too great concentration of sulphur trioxide in vented combustion gases, the sulphur trioxide causes high temperature dew point, in which the gas condenses in minute micron-size droplets of dew point product, which is substantially sulphuric acid, if the PPM of sulphur trioxide and the partial pressure of water vapor permit. As an example, when the partial pressure of water vapor is 100 MM Hg and there are 80 PPM of sulphur trioxide, dew point temperature is 282.degree. F., but at 50 MM Hg of water vapor, and 40 PPM of sulphur trioxide, the dew point falls to 253.degree. F. It is then obvious, that if the combustion gases, for discharge to the atmosphere are diluted, the dew point temperature can be depressed, to facilitate further diffusion of the sulphur trioxide into the diluting gas before dew point temperature is reached. Thus, dew point can be depressed to a point where the resulting droplets of sulphuric acid are not produced, and the plume is avoided.
This effect of dilution in avoidance of dew point, is greatly enhanced if the diluent gases can be injected at higher temperature than that of the gases to be diluted, and a still further benefit in avoidance of dew point and sulphur plume, is realized if the warmer diluent gases are injected before discharge to the atmosphere.
All discussion to this point is predicated on the theorem that the diluent gases are injected into the diluted gases at greater flow velocity for the diluent gases, than for the diluted gases. Energy for the mixture of the diluent gases with the diluted gases, which is required for the effects desired, will vary as the square of the velocity differential or as: EQU M(V.sub.2.sup.2 -V.sub.1.sup.2)/2
in the formula V.sub.2 is the diluent gas discharge velocity, and V.sub.1 is the diluted gas velocity. In a typical stack V.sub.1 exceeds 50 feet per second, and a preferred V.sub.2 would be in the order of 100 feet per second. However, a lower V.sub.2 is satisfactory so long as it significantly exceeds V.sub.1.